Estimation of stem volume in boreal forests using ERS-1 C- and JERS-1 L-band SAR data

Multi-temporal ERS-1 C- and JERS-1 L-band Synthetic Aperture Radar (SAR) da ta were analysed to determine the relationship between radar backscattering and forest stem volume. The test site is located within the boreal conifer belt in northern Sweden with stem volume in the range of 0-300 m(3) ha(-1) The statistical analysis was carried out using the water cloud model and v arious linear regression models. It was confirmed that the L-band of JERS-1 shows a consistently higher sensitivity to stem volumes in boreal forests with a larger backscatter contrast between nonforested areas and areas havi ng dense tree cover in comparison with the C-band of ERS-1. The saturation levels for the ERS-1 and JERS-1 SAR sensors were estimated at 64 m(3) ha(-1 ) and 143 m(3) ha(-1), respectively. Furthermore, the temporal analysis sho ws that the backscattering coefficient can differ by approximately three de cibels, at most, between acquisitions for a given stem volume. However, a m ajor finding is that the temporal variation could be modelled as an additiv e effect that is constant throughout the range of stem volume. For operatio nal forestry purposes this would imply that stem volume can be predicted af ter calibration of the radar response using clear felled areas as reference targets. The multi-temporal JERS-1 dataset was used to develop a radar-bas ed model of stem volume. The model was tested on a validation dataset resul ting in a correlation coefficient of 0.78 between SAR estimated stem volume and ground data.